Retainer for an adjustable balance ring in a disc clamp assembly

ABSTRACT

A disc clamp assembly and method for balancing a spindle hub assembly within a disc drive utilizes a base piece, a balance ring retainer piece and a balance ring. The disc clamp base piece is positioned on the top surface of the rotatable spindle hub to secure a disc stack to the spindle hub. The balance ring retainer piece is attached to the top surface of the base piece and defines a peripheral rim for accepting a balance ring. The balance ring has a predetermined mass to modify the center of gravity of the spindle hub assembly toward the central axis of rotation for the spindle hub.

RELATED APPLICATIONS

[0001] This application is a divisional application of U.S. patentapplication Ser. No. 09/934,164 filed on Aug. 21, 2001, which claimspriority of U.S. provisional application Serial No. 60/227,616, filedAug. 23, 2000.

FIELD OF THE INVENTION

[0002] This application relates generally to magnetic disc drives andmore particularly to a disc drive disc clamp assembly having a base,retainer and balance ring.

BACKGROUND OF THE INVENTION

[0003] Disc drives are data storage devices that store digital data inmagnetic form on a storage medium on a rotating information storagedisc. Modern disc drives include one or more rigid discs that are coatedwith a magnetizable medium and mounted on the hub of a spindle motor forrotation at a constant high speed. Information is stored on the discs ina plurality of concentric circular tracks typically by an array oftransducers (“heads”) mounted to a radial actuator for movement of theheads relative to the discs. Each of the concentric tracks is generallydivided into a plurality of separately addressable data sectors. Theread/write transducer, e.g., a magnetoresistive read/write head, is usedto transfer data between a desired track and an external environment.During a write operation, data is written onto the disc track and duringa read operation the head senses the data previously written on the disctrack and transfers the information to the external environment.

[0004] The heads are mounted via flexures at the ends of a plurality ofactuator arms that project radially outward from the actuator body. Theactuator body pivots about a shaft mounted to the disc drive housing ata position closely adjacent the outer circumference of the informationstorage discs. The pivot shaft is parallel with the axis of rotation ofthe spindle motor and the information storage discs, so that when theactuator arms are pivoted, the heads move in an arc across the surfacesof the information storage discs.

[0005] As briefly noted above, modem disc drives include one or moreinformation storage discs mounted on the spindle motor. Spacers aretypically mounted on the spindle motor between information storage discsto provide adequate separation between the information storage discs forallowing the actuator arms and the attached flexures to position twoheads against adjacent disc surfaces. The information storage discs andspacers collectively form a disc stack, or disc pack, that is mounted onthe spindle motor hub and held together with a disc clamp to form thespindle motor hub assembly.

[0006] It is critical in the disc drive industry, especially in light ofincreased spindle motor speeds, to not only have the disc stack securedto the spindle hub, but to have an overall balanced spindle hubassembly, i.e., where the center of gravity of the spindle hub assemblyis positioned at or close to the central axis of rotation of the spindlehub. Imbalance within the spindle hub assembly may cause undue anduneven wear on the spindle motor and may result in rotational vibrationswithin the disc drive. Rotational vibrations may cause undesiredvariations in the read/write signals detected by the read/write headsand may result in unwanted noise emissions from the disc drive.

[0007] The overall balance of a spindle hub assembly results fromimbalances contributed by the information storage discs, the discspacers, the hub itself, the disc clamp and the clamping force appliedby the disc clamp, or any combination of the above imbalances of theabove. Improved disc clamp design has helped improve the overall balanceof the spindle hub assembly, especially with regard to manufacturing ofdisc clamps that provide a more uniform vertical clamping force.Additionally, recent aluminum disc clamp designs have introduced abalancing structure that modifies the disc stack center of gravity to bepositioned toward the central axis of spindle hub rotation. However,these newer disc clamp designs often require complex and costlyfabrication methods.

[0008] Accordingly, there is a need in the art for a relativelyinexpensive disc clamp having a balancing structure for balancing thespindle hub assembly.

SUMMARY OF THE INVENTION

[0009] Against this backdrop the present invention has been developed.In one embodiment, the invention is a disc clamp assembly for exerting aclamping force on a disc stack to secure the disc stack to a spindlehub, where the disc clamp assembly, disc stack, and spindle hub combineto form a spindle hub assembly. The disc clamp assembly modifies thecenter of gravity of the spindle hub assembly toward a central axis ofrotation of the spindle hub, and includes a disc shaped base piecehaving a top surface and a bottom surface, the bottom surface forcontacting a top surface of the spindle hub. The base piece alsoincludes a peripherally located annular ring for contacting a topinformation storage disc of the disc stack.

[0010] The disc clamp assembly also includes a disc shaped retainerpiece engaged to the top surface of the base piece, the retainer piecehaving a peripheral balance ring receiving portion for receiving abalance ring. The balance ring having a first end and a second end witha gap formed therebetween, where the predetermined mass of the balancingring is varied dependent on the length of the balance ring. The balancering is secured within the peripheral balance ring receiving portion ofthe retainer piece to modify the center of gravity of the spindle hubassembly toward the central axis of the spindle hub.

[0011] In another embodiment, the invention is a balance ring retainerfor balancing a spindle hub assembly, and includes an annular shapedcentral web portion for operative attachment to the spindle hub and aperipheral balance ring accepting portion for accepting a balancingring. The balance ring has a first end and a second end a gaptherebetween. The length of the balance ring determines the mass of thebalance ring so that a balance ring is selected to improve the balanceof the spindle hub assembly.

[0012] Finally, an embodiment of the invention is a method of balancinga spindle hub assembly within a disc drive. The method includes thesteps of assembling a disc stack on a spindle hub of a disc drivespindle motor; assembling a disc clamp assembly having a base piece anda balance ring retainer piece; positioning the disc clamp assembly onthe spindle hub so that the base piece engages both the spindle hub anda top surface of an information storage disc in the disc stack;determining the center of gravity of a spindle hub assembly comprisingthe assembly of the spindle hub, the disc stack, and the disc clampassembly; and positioning a balance ring having a predetermined mass inthe balance ring retainer piece of the disc clamp of the disc clampassembly to move the center of gravity of the spindle hub assemblytoward the central axis of rotation for the spindle hub assembly.

[0013] These and various other features as well as advantages whichcharacterize the present invention will be apparent from a reading ofthe following detailed description and a review of the associateddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a plan view of a disc drive incorporating a preferredembodiment of the present invention and illustrating primary internalcomponents of the disc drive.

[0015]FIG. 2 is a representative cross sectional view of a disc stackillustrating a disc clamp assembly in accordance with a preferredembodiment of the present invention.

[0016]FIG. 3 is an enlarged isometric view of a base portion of the discclamp assembly shown in FIG. 2.

[0017]FIG. 4 is a cross-sectional view through the base portion of thedisc clamp taken along line 4-4 in FIG. 3.

[0018]FIG. 5 is an enlarged isometric view of a retainer portion of thedisc clamp assembly shown in FIG. 2.

[0019]FIG. 6 is an exploded view of the base portion, the retainerportion, and a balance ring of the disc clamp assembly shown in FIG. 2.

[0020]FIG. 7 is an isometric view of the disc clamp assembly shown inFIG. 2.

[0021]FIG. 8 is a cross-sectional view through the disc clamp assemblytaken along line 8-8 in FIG. 7.

[0022]FIG. 9 is a process flow diagram for balancing a spindle hubassembly in conformity with one embodiment of the present invention.

DETAILED DESCRIPTION

[0023] A disc drive 100 constructed in accordance with a preferredembodiment of the present invention is shown in FIG. 1. The disc drive100 includes a base plate 102 to which various components of the discdrive 100 are mounted. A top cover 104, shown partially cut away,cooperates with the base plate 102 to form an internal, sealedenvironment for the disc drive in a conventional manner. The componentsinclude a spindle motor 106 which rotates one or more discs 108 at aconstant high speed. Information is written to and read from tracks onthe discs 108 through the use of an actuator assembly 110, which rotatesduring a seek operation about a bearing shaft assembly 112 positionedadjacent the discs 108. The actuator assembly 110 includes a pluralityof actuator arms 114 which extend towards the discs 108, with one ormore flexures 116 extending from each of the actuator arms 114. Mountedat the distal end of each of the flexures 116 is a head 118 whichincludes an air bearing slider (not shown) enabling the head 118 to flyin close proximity above the corresponding surface of the associateddisc 108.

[0024] During a seek operation, the track position of the heads 118 iscontrolled through the use of a voice coil motor (VCM) 124, whichtypically includes a coil 126 attached to the actuator assembly 110, aswell as one or more permanent magnets 128 which establish a magneticfield in which the coil 126 is immersed. The controlled application ofcurrent to the coil 126 causes magnetic interaction between thepermanent magnets 128 and the coil 126 so that the coil 126 moves inaccordance with the well known Lorentz relationship. As the coil 126moves, the actuator assembly 110 pivots about the bearing shaft assembly112, and the heads 118 are caused to move across the surfaces of thediscs 108.

[0025] The spindle motor 106 is typically de-energized when the discdrive 100 is not in use for extended periods of time. The heads 118 aremoved over park zones 120 near the inner diameter of the discs 108 whenthe drive motor is de-energized. The heads 118 are secured over the parkzones 120 through the use of an actuator latch arrangement, whichprevents inadvertent rotation of the actuator assembly 110 when theheads 118 are parked.

[0026] A flex assembly 130 provides the requisite electrical connectionpaths for the actuator assembly 110 while allowing pivotal movement ofthe actuator assembly 110 during operation. The flex assembly includes aprinted circuit board 132 to which head wires (not shown) are connected;the head wires being routed along the actuator arms 114 and the flexures116 to the heads 118. The printed circuit board 132 typically includescircuitry for controlling the write currents applied to the heads 118during a write operation and a preamplifier for amplifying read signalsgenerated by the heads 118 during a read operation. The flex assembly130 terminates at a flex bracket 134 for communication through the baseplate 102 to a disc drive printed circuit board (not shown) mounted tothe bottom side of the disc drive 100.

[0027] One or more information storage discs 108 are mounted on aspindle hub 136 as shown in FIG. 2. A typical spindle hub assembly 138has a rotating hub 136 journaled to a non-rotating spindle shaft 140where the spindle shaft 140 is attached to the base plate 102 andanchors the rotating hub 136 within the disc drive 100. Extending from alower end of the rotating hub 136 is an annular flange 144 having aloading surface 146 for receiving a bottom information storage disc 148.An annular disc spacer 150 is stacked on the bottom information storagedisc 148. A top information storage disc 152 is stacked on the discspacer 150. The combination of information storage discs and discspacers is referred to as a disc stack 151.

[0028] A disc clamp assembly 154 in accordance with a preferredembodiment of the present invention is secured to the spindle hub 136and exerts a downward force on the information storage discs 108 anddisc spacers 150. Note that while two discs 148 and 152 are discussedfor purposes of FIG. 2, it is envisioned that one or more discs andcorresponding spacer(s) may be used with the current invention as longas the number of discs and spacers fits within the tolerance limits ofthe particular disc drive.

[0029] One critical aspect to proper disc drive operation is that thespindle hub 136, information storage discs 108, disc spacers 150 anddisc clamp assembly 154, i.e., the spindle hub assembly 138, have acylindrical symmetry about the central axis of rotation 156 of thespindle hub 136. Cylindrical symmetry of the spindle hub assembly is theresult of having a balanced spindle hub assembly 138, i.e., the centerof gravity of the spindle hub assembly 138 is essentially positioned atthe central axis of rotation 156 of the spindle hub 136. However,imperfections and cost considerations in design, manufacture and theassembly of the spindle hub assembly often result in variations in thecenter of gravity for the spindle hub assembly, thus resulting in anoff-center center of gravity for the assembly.

[0030] The present invention provides a device and method for balancingthe spindle hub assembly 138, and is implemented through embodiments ofa disc clamp assembly 154 that includes a balance feature for thespindle hub assembly 138. Embodiments of the disc clamp assembly 154 ofthe present invention provide a simple and inexpensive solution for bothsecuring the disc stack 151 to the spindle hub 136 and balancing, i.e.,aligning the center of gravity and central axis of rotation 156 of thespindle hub assembly 138, the spindle hub assembly.

[0031] Referring again to FIG. 2, a spindle hub assembly 138 is shownhaving a balancing feature in accordance with an embodiment of thepresent invention. A disc clamp assembly 154 having a base piece 158,balance ring retainer piece 160 and balance ring 162 are shown, wherethe balancing ring 162 modifies the center of gravity of the spindle hubassembly 138 toward the central axis of rotation 156 of the spindle hub136. When the center of gravity and central axis of rotation 156 of thespindle hub 136 are substantially aligned, rotational vibrations areminimized within the spindle hub assembly 138, thus reducing acousticemissions and read/write disturbances.

[0032] Preferred embodiments of the disc clamp assembly 154 of thepresent invention have a three piece design as shown in FIGS. 6-8: abottom hub-engaging base piece 158 is secured to the spindle hub 136 andexerts a downward force on the disc stack 151; an upper balance ringretainer piece 160 attaches to the base piece 158 for receiving andsecuring a balance ring 162; and a balance ring 162 is received in theretainer piece 160 for modifying the balance of the spindle hub assembly138. A mass of the balance ring 162, as determined by the total lengthof the balance ring 162, is selected for each particular spindle hubassembly 138 so as to modify the particular center of gravity for thespindle hub assembly 138 toward the central axis of rotation 156 of thespindle hub, as is discussed in greater detail below.

[0033] One embodiment of the base piece 158 of the disc clamp assembly154 is shown in FIGS. 3 and 4. The base piece 158 is generally a dischaving a central aperture 164 for mounting on the spindle shaft 140 andincludes an annular hub engagement portion 166 and a peripheral annularrim 168.

[0034] The annular hub engagement portion 166 of the base piece 158 hasflat top 170 and bottom surfaces 172, and is shaped and sized to mimicthe shape and size of the top surface 174 of the spindle hub 136 (seeFIG. 2). Six screw holes 176 are spaced an equal distance from eachother in the annular hub engagement portion 166 around the centralaperture 164, and equally spaced between every two screw holes 176 is aslot or opening 178 for engagement with the balance ring retainer 160which is described in greater detail below. Six screw holes 176 andcorresponding slots 178 are shown for illustrative purposes, althoughother numbers of screw holes 176 and slots 178 may be used in thepresent invention, where the greater number of screw holes provides fora more even load being applied by the base piece on the top surface 174of the spindle hub 136.

[0035] A series of semi-circular shaped rims 180 (FIGS. 3 and 4) extendabove the top surface 170 of the hub engagement portion 166 of the basepiece 158 to partially surround each screw hole 176. Each raised rim 180extends around an inner portion of the screw hole 176 and is positionedbetween the central aperture 164 and the peripheral rim 168. Each raisedrim 180 provides a shoulder for directly receiving/contacting a discclamp retaining screw 182 used to secure the disc clamp base piece 158to the top surface 174 of the spindle hub 136 as shown in FIG. 3. Theraised rims 180 minimize pressure hotspots on the information storagedisc formed by the downward torque of the clamp retaining screws 182, asis described and discussed in greater detail below.

[0036] The bottom surface 172 of the annular hub engagement portion 166is smooth and flat for engagement with the top surface 174 of thespindle hub 136. Six semi-circular shaped indentations 184, positionallyin-line with the raised rims 180 on the top surface 174 of the hubengagement portion 166, are defined around the inside half of each screwhole 176. The indentations result from formation of the raised rims 180.

[0037] Peripheral to the hub engagement portion 166 of the base piece158 is the annular shaped rim portion 168. When positioned on thespindle hub 136, the rim portion 168 sits beyond the outer surface 186of the spindle hub 136 and is axially aligned with the innercircumference 188 (FIG. 1) of the top information storage disc 152.(FIG. 2) As shown in FIG. 4, the peripheral rim 168 has a generallyU-shaped cross section, where the bottom of the U defines an informationstorage disc engagement surface 190 and the peripheral arm of the Uforms an upwardly extending ring of pressure lobes 192. When the basepiece 158 of the disc clamp assembly 154 is loaded on the spindle hub138, the ring-shaped information storage disc engagement surface 190extends below the hub engagement portion 166 of the base piece 158 andis coplanar with the top surface of the top information storage disc 152to uniformly engage the top information storage disc 152. The downwardtorque of the clamp retaining screws 182 into the top surface 174 of thespindle hub 136 is uniformly translated to a downward axial forcethrough the engagement surface 190.

[0038] The pressure lobes 192 of the rim portion 168 are six uniformlyshaped upwardly curved extensions, where the curve peak 196 of each lobe192 is positioned laterally in-line with the center of each of the sixscrew holes 176, and the curve minimums 198 on either side of a curvemaximum 196 are positioned laterally in-line with each slot 178. Eachpressure lobe 192 spreads and distributes the force being translatedfrom the torqued clamp retainer screw 182.

[0039] The base piece 158 of the disc clamp assembly 154 is preferablymade of aluminum, stainless steel, or another suitable malleable metal.In preferred embodiments, the base piece 158 is stamped or formed fromstainless steel sheet metal.

[0040] One embodiment of the balance ring retainer piece 160 of the discclamp assembly 154 of the present invention is shown in perspective viewin FIG. 5. The balance ring retainer piece 160 has an overall circularshape with a central aperture 200 and includes a central web portion 202spaced from a peripheral balance ring accepting portion 204 by a seriesof radial ribs or spokes 206.

[0041] The central web portion 202 of the balance ring retainer piece160 is a generally circular shape ring that surrounds the centralaperture 200. The central aperture 200 is of such size and shape so asto be snugly received by the spindle shaft 140 of the spindle hubassembly 138 and in general has a similar shape and size as the centralaperture 164 in the base piece.

[0042] In the preferred embodiment shown in FIG. 5, six equally spacedapart radially extending ribs 206 extend from the central web portion202 to the peripherally located balance ring accepting portion 204 ofthe balance ring retainer 160. The ribs are narrow strips, having flattop and bottom surfaces in-line with the central web portion 202 and theperipheral balance ring accepting portion 204.

[0043] Defined between each set of two ribs 206 in the central webportion 202 is an arcuate shaped cut-out 208. Each cut-out 208 providesaccess for one of the partially raised rims 180 that extend from thebase piece 158 of the disc clamp assembly 154 when the base piece andbalance ring retainer piece are engaged. The cut-outs 208 assists inaligning the base piece 158 with the balance ring retainer piece 160, asshown in FIG. 7.

[0044] Three male snaps 210, equally spaced from each other in thecentral web portion 202 of the balance ring retainer piece 160, protrudedownwardly from the bottom surface of the central web portion of theretainer piece 160. Each snap 210 has an opening 212 and two opposeddownwardly extending protrusions 214, each protrusion 214 of a snap 210being outwardly biased where one protrusion extends from one half of theopening 212 and the second protrusion extends from the other half of theopening 212. In use, each snap 210 inserts into one of the axiallyaligned receiving slots 178 in the base piece 158 of the disc clampassembly 154 and thereby aligns and snaps together the base piece 158 tothe balance ring retainer piece 160 of the disc clamp assembly. The snapprotrusions 214 frictionally engage the inner surface of the slots 178in the base piece 158 to hold the two pieces of the disc clamp assembly154 together. The engagement is sufficient to keep the parts togetherduring shipment, and assembly of the disc clamp assembly 154 onto thespindle hub 136. Note that other attachment means, including but notlimited to adhesives, are envisioned to be within the scope of thepresent invention, as long as the attachment is sufficient to hold theretainer piece 160 together with the base piece 158 during shipment andpresentation to the spindle hub 136.

[0045] The peripheral balance ring accepting portion 204 of the balancering retainer piece 160 has an annular shape upwardly bent rim 216 thatdefines a groove 218 for receiving and retaining a balance ring 162.

[0046] The balance ring retainer 160 may be formed from a metal such asaluminum or stainless steel, or may be formed from a plastic material.Preferred embodiments of the balance ring retainer 160 are stamped fromstainless steel sheet metal or are formed from injected molded plastic.Preferable plastics for use with the present invention do not outgas andinclude, but are not limited to, polycarbonate, PPS, and the like.

[0047] The balance ring 162 itself is preferably a flexible piece ofspring wire having a first end 215 and a second end 217. The spring wirelength is less than the inside perimeter length of the peripheralbalance ring accepting portion 204. Spring wire length for use with aparticular balance ring retainer piece 160 is determined so as to modifythe center of gravity for the spindle hub assembly 138 toward thecentral axis of rotation 156 of the spindle hub 138. Placement of thebalance ring 162 in the balance ring retainer piece 160 entailscompressing the balance ring 162 to a diameter smaller than the diameterof the balance ring retainer piece 160 and releasing the balance ring162 in the groove 218 to outwardly press against the upwardly bent rimfor frictional engagement with the balance ring retainer piece. Notethat the length of the gap between the first end 215 and the second end217 of the balance ring 162 determines the mass of the balance ring.

[0048] With reference to FIGS. 6-8, the balance ring retainer piece 160and the base piece 158 of the disc clamp assembly 154 align with eachother so that the bottom surface 220 of the central web portion 202 ofthe balance ring retainer 160 sits on the top surface 170 of the centralhub engagement portion 166 of the base piece 158. The diameter of thebase piece 158 is smaller than the diameter of the balance ring retainerpiece 160 so that the upwardly extending pressure lobes 192 at theperiphery of the base piece 158 extend upwardly into a space 222 betweenthe central web portion 202 and peripheral balance ring retainingportion 204 of the balance ring retainer 160. The maximum peak 196 ofeach pressure lobe 192 sits equally between any two radial ribs 206 thatconnect the central web portion 202 and peripheral balance ringaccepting portions 204 of the balance ring retainer 160. Additionally,as noted above, each raised rim 180 of the base piece 158 extends intothe cut-out 208 defined in the central web portion 202 of the balancering retainer piece 160. Once the base piece 158 and balance ringretainer piece 160 are engaged, each raised rim 180 extends tosubstantially the same height as the thickness of the central webportion 202 of the balance ring retainer 160 so that a top surface ofthe rims 180 are flush with the top surface of the central web portion202.

[0049] In use, the base piece 158 and balance ring retainer piece 160are snapped together and the central apertures 164, 200 for each pieceare positioned around the spindle shaft 140. The base piece 158 sits onthe top surface 174 of the spindle hub 136 so that the screw holes 176of the base piece 158 are axially aligned with corresponding screw holes224 (see FIG. 2) in the spindle hub 136. Each screw 182 is torqued intothe spindle hub 136 until the screw 182 contacts the area 226 adjacentthe cut-out 208 of the central web portion 202 of the balance ringretainer piece 160, compressing the central web portion 202 downwardonto the top surface 170 of the central hub engagement portion 166 ofthe base piece 158. Each screw 182 is torqued into the spindle hub 136until the screw head 228 comes to rest on the raised rim 180 of the basepiece 158 thereby directly applying a downward force on the base piece158 that is translated to the information storage disc engagement edge190 as an axial downward clamping force on the disc stack. Note that theraised rim 180 also evens out and distributes the force exerted by thescrew 182 onto the base piece 158 thereby providing a more uniformdownward clamping force at the periphery of the base piece of the discclamp assembly. The raised rim feature 180, in association with thepressure lobe feature 192, remove any pressure “hotspots” caused by thetorqued screws and provide for a substantially flush connection betweenthe base piece 158 and the top surface 170 of the hub, and hence a moreuniform downward clamping force on the top information storage disc 108.The uniform clamping force on the disc prevents distortion duringtemperature changes within the disc drive and is therefore advantageousto the operation of the disc drive 100.

[0050] Once the base piece 158 and balance ring retainer piece 160 aresecured to the spindle hub 138, the center of gravity for thatparticular spindle hub assembly can be determined by means well knownwithin the art. For instance, the disc stack may be spun, and theresulting forces measured with an accelerometer coordinated with anindex mark on the ring retainer. The appropriate spring wire is selectedfrom the information provided by the accelerometer, i.e., the correctmass/length of spring wire is selected, compressed into a curved ringand aligned over the balance ring retainer 160 so as to align the gap230 in the balance ring 162 in such a manner as to move the center ofgravity of the spindle hub assembly toward the center of rotation. Thecurved spring wire is compressed to a smaller diameter than the balancering retainer piece 160 diameter and released into proper position inthe peripheral ring portion 204 where the spring wire is frictionallyengaged within the groove 218.

[0051] One method for balancing a spindle hub assembly 138 in conformitywith the present invention is shown in FIG. 9. In operation 900, a discstack 151 (information storage discs and associated disc spacers) isassembled on the spindle hub 136 of the disc drive spindle motor 106. Inoperation 902, the base piece 158 and balance ring retainer piece 160 ofthe disc clamp assembly 154 are attached together through the male snaps210 on the retainer piece being frictionally engaged by the slots 178 inthe base piece. In operation 904, the assembly of the base piece and thebalance ring retainer piece is positioned over the spindle shaft 140 andon the top surface 174 of the spindle hub 136 so that the peripheraldisc engagement surface 190 is positioned against the top informationstorage disc 152 mounted on the spindle hub. In operation 906, theappropriate number of screws 182 are used to secure the spindle hub 136to the base piece 158 and balance ring retainer piece 160. In operation908, the center of gravity for the spindle hub assembly 138, i.e., thespindle hub, disc stack, base piece and retainer piece, is determined.In operation 910, a balance ring 162 having the correct mass is selectedfor balancing the spindle hub assembly. In operation 912, theappropriate balance ring 162 is positioned in the balance ring retainer160 to modify the center of gravity of the spindle hub assembly towardthe central axis of rotation of the spindle hub. Finally, the assemblymay go through a balance verification for process control.

[0052] In summary, the preferred embodiment of the invention describedherein is directed to a disc clamp assembly (such as 154) for exerting aclamping force on a disc stack (such as 151) to secure the disc stack toa spindle hub (such as 136) and form a spindle hub assembly (such as138). The disc clamp assembly (such as 154) modifies the center ofgravity of the spindle hub assembly toward a central axis of rotation(such as 156) of the spindle hub (such as 136). The disc clamp assembly(such as 154) includes a disc shaped base piece (such as 158) having atop surface (such as 170) and a bottom surface (such as 172), the bottomsurface for contacting a top surface (such as 174) of the spindle hub(such as 136), a periphery of the base piece (such as 158) having adownward extending annular ring (such as 168) for contacting a topinformation storage disc (such as 108) of the disc stack (such as 151).The disc clamp assembly also includes a disc shaped retainer piece (suchas 160) engaged to the top surface (such as 170) of the base piece (suchas 158), the retainer piece having a peripheral balance ring receivingportion (such as 204) for receiving a balance ring (such as 162). Thebalance ring has a first end (such as 215) and a second end (such as217) and an intervening gap therebetween. The balance ring (such as 162)has a predetermined mass and is secured within the peripheral balancering receiving portion (such as 204) of the retainer piece (such as 160)to modify the center of gravity of the spindle hub assembly toward thecentral axis of rotation of the spindle hub.

[0053] In other preferred embodiments of the present invention, the basepiece (such as 158) or retainer piece (such as 160) may be stamped fromstainless steel sheet metal. In an alternative embodiment, the retainerpiece may be plastic.

[0054] In another preferred embodiment of the invention, the balancering (such as 162) is a spring wire, the spring wire is curved andcompressed to frictionally sit within the peripheral balance ringreceiving portion (such as 204) of the retainer piece (such as 160). Ina further embodiment, the predetermined mass of the balance ring (suchas 162) is adjusted by varying the length of the spring wire.

[0055] In another preferred embodiment of the invention, the base piece(such as 158) includes a series of equally spaced apart holes (such as176) for receiving screws (such as 182) to secure the base piece (suchas 158) to the top surface (such as 174) of the spindle hub (such as136); and a raised rim (such as 180) partially surrounds each hole (suchas 176) to contact a head of the screw received within the hole. Inanother embodiment, the retainer piece (such as 160) has a central webportion (such as 202) defining a series of cut-outs (such as 208), eachcut-out receiving a raised rim (such as 180) from the base piece (suchas 158) so that a top surface of the retaining piece (such as 160) issubstantially flush with a top surface of the raised rim (such as 180)to allow the screw head to simultaneously secure both the base piece(such as 158) and the retainer piece to the top surface (such as 174) ofthe spindle hub (such as 136). In anther embodiment, the base piece(such as 158) may include a series of upwardly extending pressure lobes(such as 192) located about the periphery of the base piece, thepressure lobes adjacent each spaced apart screw hole (such as 176) tohelp distribute the downward force applied by the screws to the basepiece. In another embodiment, the central web portion (such as 202) ofthe retainer piece (such as 160) defines a series of equally spacedapart downwardly extending snaps (such as 210), each snap (such as 210)is frictionally received by a corresponding slot (such as 178) formed inthe central hub engagement portion (such as 166) of the base piece.

[0056] A further preferred embodiment of the invention described hereinis directed to a balance ring retainer (such as 160) for balancing aspindle hub assembly (such as 138). The balance ring retainer has anannular shaped central web portion (such as 202) for operativeattachment to the spindle hub (such as 136) and a peripheral balancering accepting portion (such as 204) for accepting a balance ring (suchas 162). The balance ring has a first end (such as 215) and a second end(such as 217), where the length of distance between the two ends of thebalance ring determines the mass of the balance ring. The mass of thebalance ring (such as 162) being selected to improve the balance of thespindle hub assembly (such as 138).

[0057] In another embodiment of the invention, the annular shapedcentral web portion (such as 202) defines a series of equally spacedapart cut-outs (such as 208), each cut-out receiving a screw foroperatively attaching the balance ring retainer (such as 160) to thespindle hub assembly (such as 138). Note also that the balance ringretainer (such as 160) may have a groove (such as 218) for frictionallythe balance ring (such as 162). Finally, the annular shaped web portion(such as 202) of the balance ring retainer (such as 162) may have aplurality of snaps (such as 210) for engaging a series of correspondingholes or slots (178) on the disc clamp (such as 158) so as to attach thebalance ring retainer to the disc clamp.

[0058] A further preferred embodiment of the invention described hereinis directed to a method of balancing a spindle hub assembly (such as138) within a disc drive (such as 100). The method includes the steps ofassembling a disc stack on a spindle hub of a disc drive spindle motor(such as in operation 900); assembling a disc clamp assembly having abase piece and a balance ring retainer piece (such as in operation 902);positioning the disc clamp assembly on the spindle hub so that the basepiece engages both the spindle hub and a top surface of an informationstorage disc in the disc stack (such as in operation 904); determiningthe center of gravity of a spindle hub assembly where the assemblyincludes the spindle hub, disc stack and disc clamp assembly (such as inoperation 908); and positioning a balance ring having a predeterminedmass in the balance ring retainer piece of the disc clamp assembly tomove the center of gravity of the spindle hub assembly toward a centralaxis of rotation for the spindle hub assembly (such as in operation912).

[0059] It will be clear that the present invention is well adapted toattain the ends and advantages mentioned as well as those inherenttherein. While a presently preferred embodiment has been described forpurposes of this disclosure, various changes and modifications may bemade which are well within the scope of the present invention. Numerousother changes may be made which will readily suggest themselves to thoseskilled in the art and which are encompassed in the spirit of theinvention disclosed and as defined in the appended claims.

What is claimed is:
 1. A balance ring retainer for balancing a spindlehub assembly, the balance ring retainer comprising: an annular shapedcentral web portion for operative attachment to the spindle hub; and aperipheral balance ring accepting portion spaced from the central webportion, the balance ring accepting portion for accepting a balance ringhaving a first end and a second end, wherein the gap distance betweenthe two ends determines the predetermined mass of the balance ring, andwherein the mass of the balance ring is selected to improve the balanceof the spindle hub assembly.
 2. The balance ring retainer of claim 1wherein the annular shaped central web portion defines a series ofequally spaced apart cut-outs, each cut-out receiving a screw foroperative attachment of the balance ring retainer to the spindle hubassembly.
 3. The balance ring retainer of claim 1 wherein the peripheralbalance ring accepting portion has a groove for frictionally engagingthe balance ring.
 4. The balance ring retainer of claim 1 wherein theannular shaped central web portion defines a plurality of snaps forengaging a series of corresponding holes in a disc clamp so as to attachthe balance ring retainer to the disc clamp.